Does Southern Ocean Surface Forcing Shape the Global Ocean Overturning Circulation?

• Published in: Geophysical Research Letters
• Main Authors: Sun, Shantong, Eisenman, Ian, Stewart, Andrew L
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2018
• Subjects: Climate Action; Life Below Water; Southern Ocean; global ocean overturning circulation; climate model; Last Glacial Maximum; Meteorology & Atmospheric Sciences; Antarc*; Antarctic; Sea ice
• Online Access: https://escholarship.org/uc/item/3kx1q270; https://escholarship.org/content/qt3kx1q270/qt3kx1q270.pdf; https://doi.org/10.1002/2017gl076437

Paleoclimate proxy data suggest that the Atlantic Meridional Overturning Circulation (AMOC) was shallower at the Last Glacial Maximum (LGM) than its preindustrial (PI) depth. Previous studies have suggested that this shoaling necessarily accompanies Antarctic sea ice expansion at the LGM. Here the influence of Southern Ocean surface forcing on the AMOC depth is investigated using ocean-only simulations from a state-of-the-art climate model with surface forcing specified from the output of previous coupled PI and LGM simulations. In contrast to previous expectations, we find that applying LGM surface forcing in the Southern Ocean and PI surface forcing elsewhere causes the AMOC to shoal only about half as much as when LGM surface forcing is applied globally. We show that this occurs because diapycnal mixing renders the Southern Ocean overturning circulation more diabatic than previously assumed, which diminishes the influence of Southern Ocean surface buoyancy forcing on the depth of the AMOC.